Image capture devices are used in a variety of devices including various cameras. For example, fixed-position cameras and pan/tilt/zoom cameras use image capture devices. The image capture devices come in a variety of forms including “global shutter” capture devices and “rolling shutter” capture devices. Global shutter capture devices capture an entire frame simultaneously while rolling shutter devices typically scroll through rows of pixels of a frame, with the capture of consecutive rows typically overlapping partially in time.
With rolling shutter capture devices, image flicker may occur due to periodic illumination either directly impinging upon the capture device or by reflection off an object in the field of view of the capture device. As the rows are scrolled through, different rows will include different portions of a cycle of the periodic illumination. Thus, stripes of relatively bright pixels and relatively dark pixels will be produced. The stripes will tend to move from frame to frame unless the image capture frequency matches a multiple of the illumination cycle.
Various techniques have been proposed to detect this flicker. For example, the flicker can be detected by taking the difference of the brightness of the same row in consecutive frames, and then looking at the difference over the vertical frame. By finding the number of peaks and valleys of the differences over the height of the frame, the frequency of the flicker is determined. Alternatively, flicker can be determined by summing the pixels in each row, and determining frequency from the product of the frame period and the AC line frequency in cycles per image frame. Alternatively still, flicker can be determined by summing the pixel intensities of rows for consecutive frames, subtracting one frame's row sum from the other, and analyzing the resulting periodic data to determine the frequency of the flicker. Further, a separate light sensor could be used to examine light intensity and identify flicker.